The Obesity-Osteoarthritis Link

I blogged a few weeks ago about yet another study suggesting that running won't ruin your knees – if anything, it will lower your risk of osteoarthritis. The presumed reason for that link is that running keeps your weight lower, and less weight means less load on your your joints. But as I discuss in my Globe and Mail column this week, it's not quite that simple:

[W]hy, then, is osteoarthritis of the hand – containing non-load-bearing joints – also twice as common in obese people?

That’s the riddle at the heart of a debate currently flaring up in academic journals, between researchers who hold the traditional view of osteoarthritis as a product of purely mechanical forces, and those who believe that inflammatory signals triggered by conditions like obesity can play a key role. [READ ON...]

The new view is that fat isn't just a blob of inert tissue; it's metabolically active, "a rich source of pro-inflammatory endocrine factors" that circulate throughout the body. The joints contain receptors that are sensitive to these inflammatory signals, and that interaction could contribute to the risk of developing osteoarthritis. There have been some suggestive studies connecting levels of fat-tissue-linked hormones like leptin to arthritis rates, even after body weight is controlled for. And there have even been some attempts – without much success so far – to reduce arthritis risk by administering drugs that block the endocrine factors or their receptors. All this research is preliminary for now, but what's most interesting to me is this shift to thinking of fat tissue as something active rather than just dead weight.